1. Field of the Invention
This invention concerns reducing power supply noise within integrated circuits, and, more particularly, concerns reducing the noise in a dynamic manner in response to events within the integrated circuit.
2. Related Art
An Integrated Circuit (IC) contains transistors connected together to implement one or more digital, analog or mixed signal functions. In addition to their signal connectivity, transistors within the IC must be supplied by a power source of a specific voltage and tolerance for proper operation of the IC. With succeeding generations of IC technology, both the number and density of transistors on an IC have increased while the power supply voltage and tolerance values have been reduced to offset increases in IC power consumption which is a function of transistor count, power supply voltage and switching frequency. With the development of higher density and higher frequency integrated circuits, it has been recognized that the switching of the thousands of transistors within the IC will create power supply noise, or rapid fluctuation of the power supply voltage within the IC. As an example of the noise generated on power supply bus networks, FIG. 1 illustrates both high frequency fluctuation in the supply voltage, which is due to variations in current demand within each cycle, and low frequency fluctuation in supply voltage, which is due to cumulative affects of current demand variation due to changes in IC function as a result program control or data sensitivity on the power supply resistor-inductor-capacitor (RLC) bus network. In past generations of IC families, the addition of passive capacitance coupling the power supply to the GROUND bus within the IC has been used to stabilize power supply voltage, however, with the trend to lower supply voltages and tighter voltage variation limits at the transistor, increased capacitor sizes are required within the IC to provide stabilization. Also, the level of power supply noise immunity is being continuously reduced. With both current and future IC generations, power supply noise induced by the switching of transistors within the IC itself can result in functional failure of the IC. As a result, power supply noise within the IC is becoming an increasingly serious problem for reliable operation. Thus, a need exists for an improved structure and method for mitigating power supply noise in integrated circuits.